In the case of metal-silica catalysts prepared by co-precipitation or wetness impregnation, a previously known technique for catalyst preparation, some disadvantages may arise in that when metal content increases, the size of particles increases and becomes uneven due to particle aggregation, and that sintering may easily occur during a high-temperature calcination at 600° C. or higher.
To overcome such disadvantages, hybrid structures between metal active materials and porous silica, which is recently used as a support in supported catalysts, have been developed, and attempts have been made for various approaches in developing core-shell or yolk-shell structures, etc (Park et al., J. Mater. Chem., 2010, 20, 1239-1246). However, the structures previously suggested have disadvantages in that the preparation processes thereof are rather complicated, and that mass production is difficult to achieve and time-consuming.
Specifically, in the case of egg-shell structures consisting of cobalt and silica as ingredients, which are known to show high activity in the Fischer-Tropsch reaction, they show advantages in the control of heat of reaction or reactant diffusion among various reactions compared to general pellet-type catalysts, and thus are widely applied (Gardezi, S. A. et. al. Ind. Eng. Chem. Res. 2012, 51, 17031712).
However, the overall particle size is very large with a size of 1 mm to 2 mm, and the shell, which comprises the supported catalyst particles, is also very large with a thickness of 0.2 mm to 0.5 mm, and thus they are unfavorable in view of dispersibility of the supported cobalt particles and in view of rapid diffusion and contact efficiency of reactants on the surfaces of the cobalt particles.